The study was carried out to investigate the prevalence, proper diagnosis and control of colmunaris disease among Nile tilapia (O.niloticus) intensivelly cultured in concerete ponds. A total of 300 0. niloticus collected throughout the seasonal diagnostic services (winter, spring summer and autumn, 75 fish/season) revealed that the prevalence of columnaris disease were 0.0, 6.7, 2.7 and 10.7% respectivelly. The most common lesions of the disease were gill congestion, fin rot, scale detachment and skin ulceration. Darkeness of the fish body and complete destruction of caudal peduncle including tail and anal fins were of unusual observation. The causative agent of the disease was identified as Flexibacter columnaris. The organism was able to produce the disease in apparently healthy O. niloticus through injured gills, but unin jured gills also appeared to be attacked at comparativelly high water temperature. The disease was controlled in the lab. by application of sulphamerazine in the fish diet and pot. permenganate to aquarium water.